1. Field of the Invention
The present invention relates to a memory device and a method of manufacturing the same. More particularly, the present invention relates to a magnetic memory device and a method of manufacturing the magnetic memory device.
2. Description of the Related Art
Magnetic memory devices, such as magnetic random access memory (MRAM), are very sensitive to a variation of resistance between cells because of weak sensing signals. Therefore, if there is a large resistance deviation between cells, it may be difficult to correctly read data recorded in the memory device.
Even if a sensing error is minimized by minimizing the resistance deviation between cells, when stability of the memory cells is not ensured, i.e., when a sufficient magnetic resistance (MR) ratio is not achieved, it may be difficult not only to correctly read data but also to correctly record data to the magnetic memory device.
Accordingly, research has been conducted into minimizing the resistance deviation between cells and ensuring stability of cells. However, a more reliable magnetic memory device has not yet been developed.
Resistance deviation between cells of the magnetic memory device and the MR ratio are directly related to characteristics of a tunneling film.
In a conventional memory device, an aluminum oxide, e.g., Al2O3, film is widely used as a tunneling film. When the tunneling film is an aluminum oxide film, it may be formed to be thinner than about 12 Å for matching a sense circuit, to have a resistance as low as about 10 KΩμm2, and to have a uniform thickness so that a resistance variation between cells is less than 2%. When a thickness deviation of the aluminum oxide film is about 1 Å, the resistance varies about by about a factor of ten, i.e., one order of magnitude. Therefore, the aluminum oxide film should have thickness uniformity so that the maximum thickness variation in the cells is less than 1 Å.
FIGS. 1 and 2 illustrate cross-sectional views illustrating a process for forming an aluminum oxide film in the course of manufacturing a conventional MRAM in which an aluminum oxide film is used as a tunneling film.
Referring to FIG. 1, an aluminum (Al) film 12 is formed on a synthetic anti-ferromagnetic (SAF) film 10. Reference numeral 12a in FIG. 1 indicates a grain boundary. During the process, the Al film 12 is oxidized through a predetermined oxidation process. As illustrated in FIG. 2, as a result of the oxidation, an aluminum oxide film 14 is formed on the SAF film 10. The oxidation of the Al film 12 starts along the grain boundary 12a and progresses into the grain, as indicated by arrows in FIG. 1. More specifically, the oxidation of the Al film 12 starts at a region 12b adjacent to the grain boundary 12a and progresses into the grain.
In the case of a conventional MRAM, the resistance of the tunneling film formed as described above varies from region to region because the oxidation of the Al film 12 does not occur simultaneously everywhere on the Al film 12.
In addition, a thickness of the Al film 12 increases during oxidation. However, the thickness of the Al film 12 after oxidation is not uniform because the oxidation of the Al film 12 does not take place simultaneously over the entire region of the Al film 12, as noted above.